A CLOSER LOOK—Bushtit

by Kimball Garrett

Originally published in the Western Tanager Vol. 46 No. 5 February 1980

Closer-Look-Bushtit-illustration-by-Kimball-Garrett

The Bushtit, a common and characteristic resident of our brushy habitats, seems a plain and uniform enough bird to allow one to forego any field identification below the species level. Its fussy four inches are a rather somber gray-brown, with no important markings. But careful study of a passing flock will reveal a distinct sexual dimorphism in eye color. Furthermore, there are two rather distinct subspecies groups of bushtits found in southern California, and occasional vagrancy of flocks means that racial identification can yield important distributional information. This month we'll take a closer look at variation in the bushtit.

Ornithologists have long noted that some Bushtits have dark eyes and others have light eyes. We now know that the dark-eyed birds include all males and nestling females, while the light-eyed birds are post-fledging females ( See Figure ). The sexes are otherwise similar, except that freshly-molted males in fall may show a pinkish suffusion on the flanks.

Bushtits of chaparral and woodland habitats on the Pacific Coast are characterized by relatively dark plumage and by brown crowns which contrast somewhat with the grayish upperparts. Coastal birds do not show contrasting auricular (ear-patch) areas. Generally quite sedentary, coastal birds (Psaltriparus minimus minimus in our area) are widespread west of the deserts. They even occur on Santa Cruz and (formerly) Santa Catalina Islands, and a recent record for Anacapa Island probably pertains to this subspecies.

Interior populations (now generally all called P. m. plumbeus, or the "Lead-colored" Bushtit) occur in our region in dry brush, pinyons, and junipers at higher elevations from the White Mountains south through the ranges of the Mohave Desert. They are characterized by a uniform gray coloration (paler than that of the coastal races), and a slightly contrasting brown auricular area ( See Figure ). They also measure slightly larger, but this difference would not be noticeable in the field. On rare occasions Bushtit flocks are noted on our deserts outside of suitable breeding habitat (for example along the Lower Colorado River). Most or all of these records probably pertain to plumbeus types, but observers are urged to scrutinize extralimital bushtits carefully.

The taxonomic demise of the "Black-eared" Bushtit should be of interest to birders because it illustrates how superficial plumage differences may be unimportant in terms of the species question. The frequency of the black-eared trait in Bushtits is clinal, with only juvenal males and occasional adult males showing it along the border ranges from extreme southeastern Arizona east to the Chisos Mountains of western Texas. At the southern tip of the species' range, in Guatemala, all young birds, and all adult males show black ears. Allan Phillips (in The Birds of Arizona) discusses in his inimitable way the historical follies of Bushtit taxonomy, and emphasizes that there is little, if any, justification for the notion that "Black-eared" Bushtits are ecologically (altitudinally) segregated from the plain-eared "species." The Bushtits of the southern California desert mountains are really just "Black-eared" Bushtits beyond the far extreme of the cline, thus the "black-eared" trait is never seen in California.

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